<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		<!-- 
		    string  number  -> boolean
		 -->
		 <script type="text/javascript">
		 	
			// var str = ""
			//  string -> boolean   非空即true
			// console.log(Boolean(str));
			// number - > boolean
			
			
			// number -> boolean    非零即true
			var number = -1
			console.log(Boolean(number));
			
			console.log("-----------------------");
			// undefined
			var u = undefined  
			console.log(Boolean(u));
			
			
			console.log("------------------");
			console.log(Boolean(null));
			
			console.log("------------------");
			console.log(Boolean(NaN));
			
		 </script>
	</body>
</html>
